Robots, and in particular industrial robots, are freely programmable, program-controlled manipulation devices. The actual robot mechanics is referred to as a manipulator. This can consist of a number of moveable, interconnected links or axes, which define the kinematic chain of the robot. The kinematic chain usually extends from the foot of the robot to the flange of the robot, or, if provided, to a tool connected to the flange.
The movement of the individual axes of a robot can take place by means of a targeted control of drives, which are connected to the individual components of the manipulator. For a movement between individual points, it is possible to predetermine, during the programming of a robot program, certain parameters such as the speed, for example.
In operation, a user can control a robot via an operating system and can set operating parameters. In particular, different operating modes can be set, such as, for example, the operating modes defined according to the safety standard EN ISO 10218-1:2006 “manually reduced speed”, in which a maximum speed of the robot flange and of the tool center point or tool working point (TCP) is limited to 250 mm/s, “manual high speed” or “automatic”, in which speeds in accordance with the programming can be travelled.
In order to ensure that in the operating mode “manually reduced speed”, for example, the flange and the TCP do not move faster than 250 mm/s, appropriate monitoring modules are implemented in the robot controller, which can trigger a suitable stop in the event that a speed limit is violated. Generally, a safety controller monitors various actual values, such as the speed of the flange, for example. If a corresponding limit is exceeded, the safety controller responds in accordance with its specifications.
In addition to the speed limits for the flange and TCP, axis-specific limits are also often defined, such as maximum axis speeds, for example. In particular in the operating mode “manually reduced speed”, a maximum axis speed is advantageous in order to protect people who may share a working space with a robot during this operating mode.
A frequent violation of monitoring limits and intervention of the safety controller can significantly compromise the operability of a robot. To prevent this, it is known from an internal method to control the robot by means of intervention in the override control, or by means of implicit control of the override value. The override itself describes a derivation of the time scale between real time and system time. For example, with a program override value of 75%, a planned path with a programmed speed of 200 mm/s would be travelled only at 150 mm/s.
In the internal method, advantage is taken of the fact that the signals between the controller and the drives are smoothed by means of a so-called axis filter. Controlling of the override value in the robot controller may result in short periods of excessive speed, which can advantageously be sufficiently smoothed by the axis filter, however, such that no monitoring limits are exceeded.
The known methods are not, however, adequate for keeping all monitoring limits clean at all times while at the same time allowing a high level of robot operability or movability. In particular, if a path movement is executed by means of a spline interpolation, in order to travel along complex space curves in a highly accurate manner, the above-described method cannot be used, since no axis filters are used in a path movement by means of spline interpolation in order to advantageously allow a precise and true travel of the robot or tool.
The objective of the present invention is therefore to provide a method which permits appropriate speed capping, in particular for a path movement by means of spline interpolation. A further objective of the present invention is to provide a method which ensures precise respecting of monitoring limits.
This and additional objectives, which will become apparent from the following detailed description, are achieved by the subject matter of the independent claims.